1010 Tyco Electronics Corp.
Data Sheet
August 2006
dc-dc Converters: 36 to 75 Vdc Input, 5 Vdc Output; 50 W to 100 W
QHW050A1-Q, QHW075A1-Q, and QHW100A1-Q Power Modules;
Design Considerations
Input Source Impedance
The power module should be connected to a low
ac-impedance input source. Highly inductive source
impedances can affect the stability of the power mod-
ule. For the test config u ra tio n in Fig ure 17 , a 33 µF
electrolytic capacitor (ESR < 0.7 Ω at 100 kHz)
mounted clos e to the power module helps ensure sta-
bility of the unit. For other highly inductive source
impedances, consult the factory for further application
guidelines.
Output Capacitance
High output current tran sient rate of change (high di/dt)
loads may require high va lues of outp ut cap a cit ance to
supply the instantaneous energy requirement to the
load. To minimize the output voltage transient drop dur-
ing this transient, low E.S.R. (equivalent series resis-
tance) cap acitor s may be require d, since a high E.S.R.
will produce a correspondingly higher voltage drop dur-
ing the current transient.
Output capacitance and load impedance interact with
the power module’s output voltage regulation control
system and may produce an ’un stable’ output co ndition
for the required values of capacita nce and E.S.R. may
be dictated, depending on the modules control system.
Variations to a module’s control system to accommo-
date larger values of capacitance a re referred to by a
’–T’ suffix to the model number. There may be several
different ’–T’ variations for a specific basic module.
The process of determining the acceptable values of
capacitance and E.S.R. is complex and is load-depen-
dant. Tyco provides Web-based tools to assist the
power module end-u ser in appraising and ad justing the
effect of various load conditions and output capaci-
tances on specific power modules for various load con-
ditions.
1. Access the web at power.tycoelectronics.com/
power
2. Under Products, click on the DC-DC link
3. Under Design Tools, click on Stability Assess-
ment
4. Various design tools will be found under the
appropriate co de. Each of th ese too ls h as ce rtain
benefits to aid in the application of the power
module to capacitive loads.
5. The Excel download file will allow calculation of
phase and gain margin for specific values of load,
including output capacitance, associated E.S.R.,
and interconnect impedance. Be sure the Analy-
sis tool-pak add-in is enabled in Excel. Tutorials
on acceptable gain and phase margin are also
available using the appropriate links.
Safety Considerations
For safety-agency approval of the system in which the
power module is used, the power module must be
installed in co mpliance with the spacing and sep aration
requirements of the end-use safety agency standard,
i.e., UL60950, CSA C22.2 No. 60950-00, and VDE
0805 (EN60950).
If the input source is non-SELV (ELV or a hazardous
voltage greater than 60 Vdc and less than or equal to
75 Vdc), for the module’s output to be considered
meeting the re qu ire m en ts of safety ex tra -lo w vo ltage
(SELV), all of the following must be true:
nThe input source is to be provided with reinforced
insulation from any hazardous voltages, including the
ac mains.
nOne VI pin and one VO pin are to be grounded, or
both the input and output pins are to be kept floating.
nThe input pins of the module are not operator acces-
sible.
nAnother SELV reliability test is conducted on the
whole system, as required by the safety agencies, on
the combination of supply source and the subject
module to verify that under a single fault, hazardous
voltages do not appear at the module’s output.
Note: Do not ground either of the input pins of the
module without groundin g one of the output pins.
This may allows a non-SELV voltage to appear
between the output pin and ground.
The power module has e xtra-low voltag e (ELV) outputs
when all inputs are ELV.
The input to these units is to be provided with a maxi-
mum 20 A normal-blow fuse in the ungrounded lead.